The four things you tell us
- Your ZIP code. This picks which house price index applies to you.
- What you paid. Your best recollection. Round numbers are fine.
- The year you bought. This is the starting point we measure from.
- What you still owe. The current balance across any mortgages on the home.
Nothing else. No name, no email, no phone number, no Social Security number, no date of birth, no income. None of it is needed to do this calculation, so none of it is asked for.
The data underneath
Every quarter the Federal Housing Finance Agency publishes the All-Transactions House Price Index. It is built from repeat sales and appraisals on the millions of mortgages bought or guaranteed by Fannie Mae and Freddie Mac, which is a large enough sample to say something meaningful about how prices in an area have moved.
We use the three-digit ZIP code series, which covers 803 areas across the United States. The release currently loaded is 2026 Q1. It is public domain United States government data, free for anyone to download and check.
FHFA labels the three-digit ZIP series developmental. Where the sample for a particular ZIP area is too small to be reliable, the figure published for that area is the index for the wider metropolitan or state non-metropolitan area instead. We pass that through rather than hiding it, and each report shows which area produced it.
The calculation
An index is a level, not a price. It is set to 100 at some base period, and only the change between two points means anything. So:
- Look up the index for your ZIP area in the year you bought. Call it A.
- Look up the index for your ZIP area in the most recent quarter. Call it B.
- Estimated value = what you paid × (B ÷ A).
- Estimated equity = estimated value − your mortgage balance.
That is the entire model. There is no machine learning, no proprietary algorithm, and nothing you could not reproduce in a spreadsheet from the same public file.
A worked example
Someone paid $310,000 in 2018 for a home in ZIP 28210, and still owes $214,000.
The index for that area has risen from its 2018 level to its 2026 Q1 level, a factor of about 1.92.
$310,000 × 1.92 =
$595,500 estimated value.
$595,500 − $214,000 =
$381,500 estimated equity, about
64% of the home.
What keeps it current
When FHFA publishes a new quarterly release, we load it and recalculate every report on the Site against the new numbers. Your report changes because the underlying measurement changed, not because anything was refreshed for the sake of it.
If you opted in to text updates, that recalculation is what triggers a message, and only when your estimate has actually moved enough to be worth telling you about. If you did not opt in, your report still updates. You just have to come back and look at it.
What this cannot tell you
This is the important section, so it is not buried at the bottom in small type.
- It is not an appraisal. It is an area average applied to a number you typed in. An appraiser looks at your actual house.
- It knows nothing about your property. Not its condition, size, renovations, lot, view, or street. Two homes a hundred feet apart can be worth very different amounts while sharing exactly the same index.
- It is only as good as your inputs. A wrong purchase price or year produces a confidently wrong estimate.
- It is always somewhat behind. The index is quarterly and published in arrears, so the most recent real-world months are never in it yet.
- It is not advice. We are not financial advisers, and nothing here is a recommendation to do anything.
Use it to watch a direction over time. That is what it is good for. For anything that turns on the exact figure, pay a licensed appraiser for the exact figure.
What happens to what you enter
Your report is stored against an unguessable link so you can come back to it without an account. Nothing you enter is sold, and nothing is shared with lenders, agents, brokers, or any other company. We do not run advertising trackers. The full detail is in the Privacy Policy, and the mobile-specific commitments are in the mobile information section.